The gas has already created enough pressure to become a gas, which is the most expandable it could turn in to. Thats what i think, hope it helps.
Your answer should be C.) +2. "All the elements in Group 2 have two electrons in their valence shells, giving them an oxidation state of +2."
Credits: https://chem.libretexts.org/Core/Inorganic_Chemistry/Descriptive_Chemistry/Elements_Organized_by_Blo...
Hopefully this has helped! :)
percentage error=difference/actual value x 100
=0.534/13.0 x 100
=4.11%